A model for the infrared dust emission from forming galaxies

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Dust plays various important roles in galaxy formation and evolution. In the early epoch of galaxy evolution, dust is only supplied by supernovae (SNe). With the aid of a new physical model of dust production by SNe developed by Nozawa et al. (N03), we constructed a model of dust emission from forming galaxies on the basis of the theoretical framework of Takeuchi et al. (T03). N03 showed that the produced dust species depends strongly on the mixing within SNe. We treated both unmixed and mixed cases and calculated the infrared (IR) spectral energy distribution (SED) of forming galaxies for both cases. Our model SED is less luminous than the SED of T03 model by a factor of 2-3. The difference is due to our improved treatment of the ultraviolet (UV) photon absorption cross-section, as well as the different grain size and species newly adopted in this work. The SED for the unmixed case is found to have an enhanced near to mid-IR (N-MIR) continuum radiation in its early phase of the evolution (age ≲ 10^7.25 yr) compared with that for the mixed case. The strong N-MIR continuum is due to the emission from silicon grains, which only exist in the species of the unmixed dust production. We also calculated the IR extinction curves for forming galaxies. N03 dust was found to yield a smaller extinction than that of T03 model. For the unmixed case, near-IR (NIR) extinction is dominated by large grains of silicon and amorphous carbon, and silicate features are less prominent compared to the curve given by T03. To the contrary, the extinction curve of the mixed case has a similar shape to that of T03. Then we calculated the SED of a local starbursting dwarf galaxy SBS 0335-052. Our present model SED naturally reproduced the strong N-MIR continuum and the lack of cold far-IR emission of SBS 0335-052. We found that only the SED of unmixed case can reproduce the NIR continuum of this galaxy. We then made a prediction for the SED of another typical star-forming dwarf, I Zw 18. The MIR continuum of I Zw 18 is expected to be much weaker than that of T03 SED. We also presented the evolution of the SED of Lyman-break galaxies. Finally, we discussed the possibility of observing forming galaxies at z ≳ 5.
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A model for the infrared dust emission from forming galaxies

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